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Science to Practice |
Department of Radiology,
Thomas Jefferson University Hospital,
Jefferson Prostate Diagnostic Center,
132 S 10th St, Philadelphia, PA 19107-5244,
ethan.halpern@jefferson.edu
SUMMARY
A method that could be used to accurately assess portal venous pressure would be valuable when diagnosing portal hypertension, evaluating patient prognosis, and monitoring the progress of therapy. Baik et al have suggested that a qualitative noninvasive Doppler US parameter can be used to monitor therapy of portal hypertension. Further clinical investigation is needed to confirm these results and to determine whether hepatic venous Doppler waveform tracings can be used to monitor patient response to therapy. Ongoing research suggests that microbubble contrast agents may enable a more quantitative noninvasive estimate of intravascular pressures with US.
THE SETTING
In the setting of cirrhosis, measurement of portal venous pressure is clinically important when diagnosing portal hypertension, estimating the likelihood of variceal bleeding, and monitoring the progress of therapy. Portal pressure is a more important predictor of morbidity and mortality than is the Child-Pugh score. The reference standard for measurement of portal venous pressure is the hepatic venous pressure gradient, which is calculated by subtracting the free hepatic venous pressure from the wedged hepatic venous pressure. Unfortunately, calculation of the hepatic venous pressure gradient is invasive and expensive, and it cannot be used to monitor therapy because more than one measurement is required. An accurate noninvasive technique that could be used to measure portal venous pressure would represent a major advance in the diagnosis and management of portal hypertension. In this issue of Radiology, Baik et al (1) confirm a positive correlation between the loss of pulsatility in the hepatic venous Doppler waveform and an increase in the hepatic venous pressure gradient.
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The normal hepatic vein Doppler waveform tracing reveals variations in central venous pressure during the cardiac cycle. Hepatic venous flow is triphasic, with flow toward the heart occurring during atrial and ventricular diastole and flow away from the heart occurring during atrial systole. Hepatic venous flow patterns are altered by changes in intrathoracic and intraabdominal pressure during respiration and by changes in right-sided cardiac pressures, tricuspid insufficiency, or cardiac rhythm disturbances. Cirrhosis and portal hypertension are associated with a loss of pulsatility within the hepatic veins that is commonly attributed to hepatic fibrosis and a loss of compliance within the liver that results in narrowing of the hepatic veins (2,3).
Baik et al (1) showed that monophasic hepatic venous flow was associated with severe portal hypertension (hepatic venous pressure gradient > 15 mm Hg). More importantly, they showed that after administration of terlipressin (a vasoconstrictor that affects splanchnic circulation), baseline hepatic vein waveforms regained pulsatility and a triphasic appearance concomitant with a reduction in portal pressure. Terlipressin reduces portal venous blood flow and pressure; however, it does not alter the structural properties of the liver, and it should not change hepatic venous compliance. Thus, normalization of hepatic venous Doppler waveform tracings after intravenous administration of terlipressin suggests that the Doppler waveform changes are related to portal flow rates or pressures rather than to fixed structural changes in the liver.
THE PRACTICE
Clinical Use:
Numerous researchers have suggested that hepatic venous Doppler waveform tracings might be used to estimate portal venous pressure. Unfortunately, the practical clinical utility of such tracings is limited by intra- and interpatient variations in the appearance of the normal hepatic vein Doppler waveform. Nonetheless, the findings of Baik et al (1) indicate that sequential hepatic vein Doppler US is an effective noninvasive method that can be used to monitor the treatment of portal hypertension. Successful application of hepatic venous Doppler waveform tracings to monitor portal hypertension may be possible when variation in Doppler waveforms is minimized by obtaining sequential studies in an individual with a fixed technique. Once other researchers confirm this result, hepatic venous Doppler waveform tracings may be of great clinical value to the titration of medications administered to treat portal hypertension.
Future Opportunities and Challenges:
Accurate noninvasive measurement of portal venous pressure with ultrasonography (US) is an important objective. The findings of Baik et al (1) confirm the findings of prior studies that demonstrate a substantial overlap in measured hepatic venous pressure gradients among patients with triphasic, biphasic, and monophasic Doppler waveforms. Given the numerous factors that affect the appearance of the hepatic venous Doppler waveform, qualitative assessment of the Doppler waveform may not provide an accurate quantitative assessment of portal venous pressure. New methods for the assessment of intravascular pressure have been described. These methods are based on the shift in resonance frequency of US microbubble contrast agents as a function of pressure (4) and the relationship between the disappearance time of microbubbles and ambient pressure (5). Forsberg et al (6) proposed a method to measure intravascular pressure that was based on changes in the amplitude of the reflected subharmonic signal from microbubble contrast agents with ambient pressure.
FOOTNOTES
See also the article by Koo Baik et al in this issue.
References
Related Article
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